请分析回答（以A和a表示有关基因）

已知函数$f\left(x\right)=\cos x,x\in \left(0,2\mathrm{\pi }\right)$有两个不同的零点$x_1,x_2$，且方程$f\left(x\right)=m$有两个不同的实根$x_3,x_4$.若把这四个数按从小到大排列构成等差数列，则实数$m$的值为

My Forever Valentine

    Valentine's Day was the time my father chose to show his love for the special people in his life. Over the years I fondly (天真地) thought1him as my “Valentine Man”.

    My first recollection of the2he could bring to Valentine's Day came when I was six. That morning at the breakfast table I found a card and a gift­wrapped package at my chair.

    The card was3“Love, Dad ”and the gift was a ring with a small piece of red glass to4my birthstone, a ruby (红宝石). There is5difference between red glass and rubies to a child of six, and I remember6that ring with pride that all the cards in the world7not surpass (超越).8I grew older, the gifts gave9to heart­ shaped boxes filled with my10chocolates and always included a 11card signed “Love，Dad”. In those years my “thanks” became12of a perfunctory(敷衍的)response. The cards seemed less13and I took it for granted that the Valentine would14be there. I had15my hopes and dreams in receiving cards and gifts from “significant others” and “Love, Dad” just didn't seem quite16

    His final card remains on my desk today. It's a17of how special father can be and how important it had been to me over the years to know that I had a father who continued a 18of love with simple acts of understanding and an ability to express happiness over the people in his life.

    Those things never19nor does the memory of a man who never20being my Valentine.